A long standing issue of modulation of ascending sensory information is the action of the thalamic reticular nucleus (TRN) on the transmission of visual information through the lateral geniculate nucleus (LGN) to visual cortex. Acting on the LGN is the thalamic reticular nucleus (TRN) which receives topographically organized collaterals from both thalamus and cortex and sends similarly organized projections back to LGN. The inputs to the TRN are excitatory, but the output back to the thalamic relay is inhibitory (GABAergic), providing an ideal organization for modulating visual activity during early processing. This functional architecture led Crick in 1984 to hypothesize that TRN serves to direct a searchlight of attention to different regions of the topographic map, but in spite of the substantial influence of this hypothesis, the activity of TRN neurons has never been determined during an attention task.[unreadable] Kerry McAlonen, James Cavanaugh and I have recorded the modulation in the visual response of TRN neurons as monkeys shifted attention. Because of the multimodal nature of TRN, and the evidence of cross-modal interactions from histological studies in the rat [mcA, we used a task that required the monkey to shift attention between visual and auditory stimuli. In the awake monkey, we found that visual TRN neurons had a strong (194 spikes/s) and fast (25 ms latency) transient increase of activity to spots of light falling in their receptive fields, as well as a high background firing rate (45 spikes/s). When attention shifted to the spots of light, the amplitude of the transient visual response typically increased (on average by 10%), while other neuronal response characteristics remained unchanged. [unreadable] In sum, our experiments are the first to investigate TRN neurons in the awake monkey and they have revealed two salient characteristics of TRN neurons. First, the visual response is a remarkably consistent transient response superimposed on substantial background activity. The high background activity we observed in the TRN of the awake monkey is consistent with its potential role of providing inhibitory modulation to the LGN. Second, when the monkey shifts attention from the auditory to the visual stimulus, the amplitude of this transient response changes. If we assume that the TRN affects early visual processing by its inhibitory influence on the LGN, then the predominant attentional effect acting through the TRN in these experiments transiently increases the inhibitory GABAergic drive on the LGN.